Frequency converter



H. M. STOLLER FREQUENCY CONVERTER Filed Sept. 20, 1916 n iii /n ven for:Ha qh M. SIM/er.

Patented Oct. 27, 1925.

UNITED STATES 1,559,295 PATENT OFFICE.

HUGH M. STOLLER, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRICCOMPANY, INGORPORATEJLOF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

FREQUENCY CONVERTER.

Application filed September 20, 1916. Serial No. 121,171.

To all whom it may concern:

Be it known that I, HUGH M. STOLLER, a citizen of the United States,residing at New York, in the county of New York and State of New York,have invented certain new and useful Improvements in FrequencyConverters, of which the following is a full, clear, concise, and exactdescription.

This invention relates to frequency converters, and more particularly toa static or transformer type of converter, the object of which is toraise or lower the periodicity of a given generated alternating currentwithout resorting to the use of rapidly moving mechanisms.

This invention therefore comprises a static transformer having polyphaselow frequency windings arranged according to the practice common ininduction motor design to produce a rotating magnetic field. By an unequal distribution of the low frequency windingswith respect to thewinding space which they occupy, this rotating field is made to set upan electromotive force of higher frequency in a secondary circuit whichhas several reversals in the direction of winding so that each elementof the magnetic field, during a complete rotation of the field as awhole, has several effective reversals of direction with respect to thesecondary circuit. One revolution of the magnetic field may thereforeproduce several reversals of currents in the high frequency winding, andan arrangement is available whereby a primary current of givenperiodicity may induce a secondary current whose periodicity may be madegreater or less than the primary periodicity depending on the ratio ofprimary to secondary poles.

The invention will be more clearly understood by reference to theaccompanying drawings in which Fig. 1 illustrates the transformer ofthis invention in assembled from; Figs. 2, 3 and 4 illustrate therelative geometrical relations of the different phases of a three-phaseprimary winding; Figs. 5, 6 and 7 illustrate a geometrical arrangementof secondary windings for 1producing a three-phase secondary currentaving a frequency three times that of the primary current: Fig. 8illustrates a winding arrangement for one of the rimary phase windingsof Figs. 2, 3 or 4; Fig. 9 illustrates diagrammatically a lap windingarrangement for the windings of Figs. 5, 6 and 7; and Figs. 10 and 11illustrate the preferred connection for the primary'and secondary phasewindings respectively.

In the particular embodiment of this invention herein illustrated, aring sha ed magnetic core 1 is provided with a pluraiity of projectingteeth 2 and intervening winding slots 3. Each of the primary windings 4,5 and 6 has a section on opposite halves of the core 1, the two sectionsbeing wound in opposition, as illustrated in Figs. 2, 3 and 4,respectively. Each of these primary sections' is of the tapered type, bywhich is meant a winding in which the number of turns per unit length ofwinding space is greatest at the middle of the winding space anddecreases in order as the end of the winding space is approached. Centerline A-A of Fig. 2 indicates the general direction of the flux set up inthe space included within the ring by current in the primary winding 4,and the line about which the flux is symmetrically disposed.

It is well known that a substantially uniform rotatingmagnetic field maybe established by polyphase current supplied to corresponding polyphasewindings arranged about a core consisting of an iron ring or toroid. Ifthe individual windings are each wound according to a sinusoidaldistribution and the points at which the windings are most concentratedare equally displaced angularly about the core, the effect of thetapered windings of the type shown in Fig. 8, acting alone, is toproduce a substantlally uniform rotating field throughout the spacewithin the ring 1. With respect to the effective lines of force cuttinga conductor element of the secondary winding, the field may be viewed atany instant as a unidirectional field extending in the same direction asthe diameter of the rin passing through the conductor element. finsunidirectional field would normaly be of uniform flux density. A core ofmagnetic material within the ring, due to its lower reluctance, maymodify the flux distribution in a. manner depending upon the form andsize of the core. If there is a comparatively large air-gap, the part ofthe air-gap cut off by a tangent to the core parallel to the directionof the field will have a less dense flux, while the remainder or centralportion of the field will have a more concentrated flux. The larger theair-gap, the greater is the proportional constriction of the effectivefield, although any size of air-gap, or in fact any other'ex edient,which will tend to make the uni irectional effective field non-uniformacross the diameter, whether causing it to be constricted toward, ordispersed from the center, will give a series of electromotive forcecomponents in each winding, having a summatlon or resultantelectromotive force changing in direction as the resultant fieldreverses its direction of motion with respect'to the secondary winding,that is, every 180 electrical degrees of the secondary.

If a sinusoidal distribution of secondary winding similar to that of theprimary winding were employed, each magnetic line of force rotating at auniform angular rate would induce an electromotive force of sine waveform in the secondary Winding since the product of flux and number ofconductors would be a function of the sine of the angle traversed. Thesummation of a series of such electromotive force components differingin phase such as would be produced by the successive lines of a band offlux would also be a sine wave of the frequency of its com onents.Sinceflthe single line'of force in t e case of a secondary windinghaving six reversals changes its effective direction six times during asingle revolution, there will be an electromotive force of triplefrequency induced in the secondary winding. In the case of a uniformlydistributed winding, such as illustrated in Figs. 5, 6 and 7 of thedrawing, each line of force will generate a uare-topped .wave, but thesum of a series (if such square-topped waves will be a periodic wavedeparting to some extent from sine wave form, but still of triplefrequency.

The primaries are preferably ring wound, as shown in Fig. 8, whereas alap winding arrangement is better suited to the requirements of thesecondary. Such an arrangement for a three-phase secondary applied to acore having thirty-six winding slots is shown in Fig. 9. Thisdisposition of windings will produce a secondary frequency of threetimes the primary frequency. Figs. 5, 6 and 7 show an equivalent ringwinding arrangement of the three secondary phases 7, 8 and 9. Here itwill be noted that each secondary phase winding has six sections, threeon each half of the core, and that adjacent sections are wound inopposite directions. It will further be noted that opposite sections arewound in opposite directions so that a diametric field rotating withinthe core 1 will produce additive effects in the diametrically opposedsections. Furthermore, for each complete rotation of the field threereversals of current will result in each secondary phase winding, thusproducing a tripling of the primary frequency.

It is obvious that by employing a greater number of secondary windingsections a greater increase in frequency could be effected. Suchincrease is subject to the limitation imposed by the difliculty ofconstricting the effective rotating field to a suflicient- 1y narrowpath. The effective width of the rotating field should, in fact, becomparable to the pole width ofthe sec dary winding. Where a greaterincrease in requency is desired, it will in general be found morepracticable to connect a number of small ratio converters in tandem.

A central core member 10, is shown in Fig. 1 as located within the coremember 1. This core member 10 is preferably made of laminae oftransformer iron and serves the obvious purpose of decreasing thereluctance of the path transversed by the rotating flux. It is separatedfrom the teeth 2 by an air gap 11. The width of the air gap will vary indifferent transformers. The use of a wide air gap will cause a lowprimary power factor whereas a small air gap will cause a largesecondary reactive drop.

In general, the air gap used will be large as compared with that used indynamo-electric machinery for it here serves as a means for a disturbingthe uniform distribution of the effective field and for renderingnegligible the reactive drop due to the secondary current.

Figs. 10 and 11 illustrate the connections for the primary and secondarywindings, respectively. The disposition of the terminal portions ofadjacent sections of the windings indicates a reversal of the directionsof winding, going from one section to an electrically adjacent section.

While in the embodiment of the invention herein illustrated anddescribed both the primary and secondary windings are shown as appliedto the core member 1, it will readily appear to those versed in the artthat these windings might. so far as theoretical I10 considerations areconcerned, be equally well applied to the core member 10, or in fact oneset of windings might be applied to one core member and the other set ofwindings to the other core member without departing from the spirit andscope of the invention.

What is claimed is:

1. A frequency converter having two concentric core members separated byan air gap, tapered polyphase primary windings on one of said membersfor producing a rotating magnetic field across said gap, means forsupplying alternating current to said primary windings and a multipolarsecondary winding in the path of said rotating field, said secondarywinding servin when alternating current is supplied to said pri marywinding, as a source of alternating current of a frequency which is amultiple of that supplied to said primary winding.

2. A frequency com'erter comprising a magnetic core, polyphase primarywindings and niultipolar secondary windings on said core. said primarywindings being unequally distributed and means to produce a nonuniformrotating magnetic iield when polyphase current is supplied to saidprimary windings.

3. A frequency converter comprising a closed magnetic core, polyphaseprimary windings on said core, each phase winding having two sectionsoppositely wound on opposite halves of said core, the number of turnsper unit of core length being greatest at the middle point of said corehalves. and a secondary winding on said core, the number of poles insaid secondary winding being a multiple of the primary poles.

4. In a static frequency transformer having means for producing a rotarymagnetic field and windings inductively subjected to the influence ofsaid magnetic field, means for rendering negligible the reactive dropdue to currents generated in said windings and a magnetic coreassociated with said windings and separated therefrom by a nonmagneticgap.

5. A static frequency converter comprising a primary winding excited bycurrent of a given frequency for producing a rotating non-uniformmagnetic field, and a secondary winding associated with said primarywinding wound in successively opposed portions whereby an electromotiveforce of a fre-v quency other than that used in exciting the primary isinduced therein by said rotating field.

6. In a static transformer, means for producing a non-uniform magneticfield which rotates, said means comprising a plurality of taperedwindings and a magnetic device having a large air-gap associatedtherewith.

7. The combination of two concentric core members stationary withrespect to each other and separated by an air gap, polyphase primarywindings on one of said members for producing a rotating magnetic fieldacross said gap, and a secondary winding in the path of said rotatingfield, the number of poles of said secondary winding being a multiple ofthe number of poles of the primary winding.

8. In a static frequency transformer, an annular ring, a multi-phaseprimary winding arranged thereon to produce a rotating field within saidring, a secondary winding associated with said ring and having aplurality of poles across which said rotating field successively sweeps.and a core member within said ring spaced therefrom by a nonmagneticgap, the numbers of poles of said secondary and primary windings havinga multiple relation with each other.

9. In a static frequency converter, means for producing a rotatingnon-uniform magnetic field comprising a primary winding, anda secondarywinding associated therewith, the number of poles on one of said primaryor secondary windings having a multiple relation with respect to thenumber on the other.

In witness whereof, I hereunto subscribe my name this 19thday ofSeptember, A. D. 1916.

HUGH M. STOLLER.

